Radio receiving apparatus



Aprile, 1929.- AgN. GOLDSWTH 1,708,539

RADIO RECEIVING APPARATUS -April 9, 1929. A. N. GOLDSMITH RADIO RECEIVING APPARATUS Filed Feb. 19, 1923 10 Sheets-Sheet -2 April 9, 1929 A. N. GoLDsMrrl-l 1,708,539

' RADIO RECEIVING APPARATUS Filed Feb. 19, 1923 10 vSheets-Sll-eec, 3

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RADIO RECEIVING APPARATUS l Filed Feb.;19, 1925 10 Sheets-Sheet 4 gnou/woz pril 9, 1929.

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RADIO RECEIVING APPARATUS Filed Feb. 19, 1923 10 Sheds-Sheet. 5

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QR E5@ 526523 odin mm wm 'Patented Apr. 9, 1929.

UNITED STATES ALFRED N. GOIiDSMITH, OF MOUNT VERNON, NEW YORK, ASSIGNOR T RADIO COR-- PATENT oFFicE".

PORATION 0F AMERICA, A CORPORATION OF DELAWARE.

RADIO RECEIVING APPARATUS.

4 Application led February 19, 1923.l Serial No. 619,847.

The present invention relates to radio Vreceiving apparatus and particularly to an arrangement which may be readil used by a person comparatively unskilled in the use of radio signalling apparatus to accomplish reception of damped, undamped or interrupted continuous waves of long and short wave lengths. Certain features of theapparatus 'to be disclosed herein are'described and claimed in a copending application of Lazarus Shapiro, Serial No. 637,024 filed May 5, 1923.

In various kinds of service, such as that of the marine and signal corps, it is desirable to be able to receive signals of the various kinds mentioned above and to shift from the reception of one to the other without delay. It is also desirable in the interest of economy and portability to accomplish this without duplication of apparatus. AIt is furthermore desirable to simplify the tuning so that the adjustments necessary are as few as possible and the operation is suliiciently simple so that little training is required.

One of the objects of the present invention is to secure an arrangement fulfilling the above requirements. Further objects of the invention are to secure improved structural features such as the inductance and coupling units,the arrangement and structure for varying the tuning, the disposition of the component parts and other arrangements which will be referred to in detail hereafter. Y

The novel features which 1 believe to bek characteristic of m invention are particularly set forth in t e appended claims, the invention, itself, however, both as to its rconstruction and mode of operation, to-

gether with further objects and advantages thereof will best be understood by reference to the following description taken in connection with theaccompanying drawings in 45 which:

Fig. 1 is a diagram of the circuit arrangement.

Fig. 2 is a simplified diagram showing the circuit arrangement when receiving continuous waves.

Fig.4 3 is a simplified diagram showing the circuit arrangement when receiving interrupted or modulated continuous waves and spark or damped waves.

Fig. 4 is plan view of the receiving apparatus with the top, sides and rear end removed.

Fig. 5 is a side View ofthe arrangement shown in Fig. 4.

6 is a front view:

Flg. 7 is a detail view showing the pointer construction.

Fig. 8 is a fragmentary cross section showing a suitable construction ofthe main adjusting knob, bearing and gear.

Fig.. 9 is a detail of a collar used in the adjusting mechanism of Fig. 8.

. Fig. 10 is a fragmentary-view of the gearing arrangement.

Fig. 11vis a detail illustrating a suitable construction of a switch for the circuits.

Fig. 12 is a plan view of one of the coil units used in the arrangement for the primary 'and secondary coupling, the feed back, and as a shield. 12Fig. 13 is an end view of the unit of Fig.

Fig. 14 is a plan view of the coil and Fig. 15 is a diagram showing a convenient method of winding the coil.

Fig. 16 is a view of the sheet for holding the coil.

Fig. 17 is a view of one of the panels between which the coil units are mounted.

Fig. 18 is a plan view of a shield plate used for varying the inductance of the coils in timing, parts of the supporting and gearing mechanism being shown.

Fig. 19 is a detail viewpar'tly in cross section showing certain features of the construction of the condenser.

Figs. 2O and 21 are end views of the condenser.

Figs. 22 and 23 `are plan views showing the special shape of the stationary and movable plates of the condenser.

Fig. 24 is a diagram of a modified shield for a coil for use with a variable condenser having any desired shape of plates, and Figs. 25, 26 and 27 show the shield and coil in successively different positions.

Fig. 28 is a front view and Fig. 29 is a side view of a modification in which the condenser and shields are on the same shaft.

Figs. 30 and 31 are curves showing inductance of the shield and the capacity of the condenser for various angular positions.

The arrangement in accordance with the invention is adapted to receive telegraph signals either on continuous waves or spark a to spark reception or its equivalent.

transmission. As is well known a'receiver of spark transmission is also adapted to receive radio telephonyand interrupted continuous wave telegra h communications and the arrangement is tliierefore a universal receiver as far as the kind of transmission vis concerned. Means are also provided for readily receiving short or long Waves of either character. As shown in Fig. 1,.only a single adjuster is utilized for tuning. This consists of the adjusting knob 1 which is mechanically connected to a variable condenser 2 and a variable inductance 3 (Figs. 2 and 3) consisting of a number o coil units 3s1 382 3m 31.2a 31.3, 31.4, 3115, 3mi, 3L?,

and 3W (Fig. l) formingfthe antenna coupling coil.

A single member 4, such the reception to b e changed to either continuous wave telegraphic reception (C. W.)

Similarly a single member 5 enables reception of either long or short waves. rlhe adjustments mentioned are all that are essential, although with vacuum tubes it is also advantageous to provide an adjustment of the filament voltage, for example by means of adjustment 6 in F ig. l which acts in conjunction with rheostat 7. As the members 4 and 5 are double throw switches they do not require tedious adjustment by trial. The operation of the apparatus therefore requires trial adjustment of knob 1 and adj ustment of rheostat 7 to secure the optimum signal strength. As only one main adjustment is required 1 term my device a punicontrol receiver.

The particular embodiment of the invention illustrated by the apparatus shown in the drawing comprises terminals 8 and 9 to which the antenna 10 and ground 11 are respectively connected. The antenna terminal 8 is connected tol one terminal of the variable condenser 2 through lead 8 and the ground terminal 9 through lead 9 to the negative terminals of a filament battery 12 and a plate battery 13 for supplying current to vacuum tubes in a manner which will be more fully described hereinafter. 13etween the antenna and ground the antenna circuit is through variable condenser 2 leads 27, 28 and coils 331, 332 and 3s3 to a pivot terminal 14 of a double pole double-throw switch 15 which is controlled by the member 5. For short waves the antenna circuit will be completed to the ground terminal when the arms of switch 15 are moved upward, the connection being through switch terminals 16, 16 which are connected by a short circuiting wire, pivot terminal 14 and conductors 17, 18 and 19.

The antenna circuit for long waves is the same as for short waves except that by throwing the arms of switch 15 downward the additional coil units 3m, 3W, 3L", 3L,

as a knob enables I31', 3L, 3m, 3, 3L", and 3L10 are inserted between terminals 20 and 20 by way of conductors 21 and 22.

rlfhree vacuum tubes are utilized for the reception, preferably of a miniature type (peanut tubes) requiring a small filament current which may be obtained, for example from two standard one and one-halt` volt six inch dry cells. The first tube in accordance with the invention is utilized for C. W. reception as an oscillator for generating a heterodyne to give a beat note and for spark reception as a radio frequency amplifier. All of the Elements are heated from battery 13 b connecting one end of each filament to con uctor 18 which leads to the negative terminal by way of conductor 19 and by connecting the other ends of the filament to conductor 49 which leads to potentiometer contact 6. The filament circuits are opened and closed byl means of one arm of a three pole double throw switch 31 which has a pivot terminal 30 connected through con ductor 70 to the positive terminal of the lilament battery 12. Conductor 70 is connected toI conductor 71 by either terminal 32 or 72 of switch 31, the latter terminals being connected together. The potentiometer is connected between conductor 71 and conductor 49.

For the four possible combinations, viz (1) short wave C. W., (2) long wave C. W., (3) short wave-spark and (4) long wavespark, the circuit-s are as follows (l) Short wave, 0. W.From grid of tube 23 through conductor 73 to pivot terminal 24 of two pole double throw switch 25 to switch terminal 26 when the arms of said switch are moved up by member 4 through conductor 28 to and through primary coils 351', 3s2 and 3s3 and to ground through the short wave switch 15 the circuit therethrough being the same as that of the antenna. As simplified in Fig. 2 the circuit is from grid of tube 23 through coil 3 to ground. The condenser 2 and the antenna capacity to earth together with the primary coils form an' oscillation circuit in the grid circuit which determines the frequency of the oscillations generated by the valve. This is one important feature of the invention as by this means a single tuned circuit determines the tuning of the aerial `tuned, but this is unimportant compared to the simplification obtained by using only a single tuned circuit. The output or plate circuit of tube 23 in whichv the heterodyne frequency is repeated comprises conductor 29, pivot terminal 30 of a three pole double throw switch 31 controlled by arm 4, upper terminal 32 of switch 31, conductor 33, coil units 34, 34, 34T", 34"`4, 34T5 and 34'm in inductive relation to coils 3m, 3m, 3m, and 3TA to providea feed back between the grid and plate circuits, coil unit 35 forming additional feed back coupled to primary coil 353, conductor 36, terminal 32 vof Aswitch 31, conductor 37, plate battery 13, conductor 19 and conductor 18 connected to the filament of the valve 23. It will be noted that transformer 38 between the first and second tubes is notl utilized for this connection. The received signal with the over laid heterodyne is impressed on the grid of a second tube 3.9 serving as a radio frequency amplier through the following lcircuit; gridV of 39,

conductor 40, pivot terminal 24 of `switch 25, terminal 26', conductor Y41', secondary coil units 42, 43 inductively coupled to^primary coil unit 3s'1, conductor 44, pivot ter-- minal 45 of a second double pole double throw switch 46 controlled by member '5, up'

per terminals 47, 47- connected by a shorting wire, conductors-'48 and 49, to the lila'm'ent of valve 39. An additional coil unit 62 which serves as a shield between the primary and secondary `is arranged between the .coil unit 381, and coil unit 43 and has one terminal extending from the open and the other connected to ground through conductors 63, 64 and the conductors 18 and 19. This method of shielding which is especially convenient and eiiicient prevents undesired .capacity coupling effects. The output or plate circuit of the second valve 39 1s coupled to the input or grid circuit of a third valve 50 by means of a second transformer. The primary 51 of the latter is connected to a lead 53 extendingv .from the plusterminal of plate battery 13 'and its secondary 52 is connected to conductor 49 otentiometer contact 6. The primary an secondary windings are preferably connected by means of condenser 54, the transformer for example, being made of resistance wire Iin accordance with the inventionv disclosed in the .application of H. J: Round, Serial No. 370,175

' which provides-.resistance and inductive coupling between the tubes. The third tube is c onnected to operate as a detector, for

example by utilizing'Y fai grid condenser 55 and a grid lead 56.5-- Telephone terminals 57 and 58 are connectedafespectively to the plate of'valve 5() and "conductor 53 by lmeans of conductors 59 and 60, a telephone condenser 61 also being connected between said ter- 'minals.

To summarize the circuit for short wave C. W. utilizes ,(1)k an oscillator for generating a heterodyne, the yoscillating circuit thereon being the same' asthe oscillatin g circuit ofthe lantenna; (2') a: radiofrequen'cy amplifier and (3) adetector.

(12) Long wa/ve U. W.-When the controlling .member 5' is moved so that the arms of switches 15 and 46 are down the variable lnductance 3 is increased through switch 15 by including the coil units 3L1 to 3W between the terminals 20 and 20 as previously described,-thus giving the necessary inductance for long waves to the antenna circuit, which in this case is also the heterodyne oscillator circuit as described with reference to short wave C. W. By means of switch 46, addltional secondary -coil units 65, 66 and 67 lnductively related to coil unit 3W are connected between pivot switch terminals 45 and 45. The latter connect through the arms of switch 46 with switch terminals 68,

,68'` and in this manner the inductance of a the feed back or tickler for the long as Well as the short waves. As the circuit arrangement and the operation on long wave C. W. is the same as on short wave Cl lV. except in the particulars described, further description will be unnecessary.

(3) Slam-t wave, spar/:.-Whcn .the mem'- ber 4 is moved so that the arms of double pole double throw switch 25 andthree pole double throw switch 31 are moved down to the position for spark reception,I the-following changes will'be made in the circuit as compared with that for vshort wave, C. W.

(a) The grid `of tube 23 will be disconnectedfrom the circuit of the primaryQcoil units 331- etc. and connected through conductor 73, pivot terminal 24, terminal 74, con.- ductory 75, terminaly 26', conductor 41 to the secondary coiljunits 43, 42, conductor 44, through the short wave switch 46 to therheo'stat 7, conductorV 71, terminals 32" and y 30 of 'switch 31 to the positive terminal of the filament battery 12.

(b) The. plate of tube 23v will be diseon nected from the feed back c oils units 35, 34T, 34T, 34., 34u, 34112, 34111, leaving the circuit of the tickler element open between vterminals 30, 32 and 30", 32 and out of service.l 'The' plate' will be connected through conductor 29, pivot terminal 72conductor 76 to theprimary 38 of transformer 38 which is connectedto the plus terminal of the plate battery 13. Changesv (a) and (b) convert the rst tube Vfroman oscillator into a radio frequency amplifier. i, v

(c) The grid of the secondtube is disconnected from the secondary coils 43, 42 andthe conductor 40 leading from this grid is connected to terminal 74 which has a lead 77 connected to the secondary 38 of transformer 38. Transformer 38 is a radio frequency transformer of the same type as 51, 52, 54 and likewise has a condenser 78 across the windings.

The grid, plate and filament circuits of tube 50 are the same for spark as for continuous wave signals and the function is the same.

Briey stated the circuit arrangements convert the tube circuits from oscillator, am-

plifier and detector for C. W. to amplifier,

amplifier and detector for spark signals, and utilize all of the elements for both C. W. and spark except the feed back coils and one radio frequency transformer.

Long 'wa/ve, .spark- The circuit arrangement in this case is the same as that for short wave spark, except that the inductance 3 is increased by connecting coil units `3L1 to 3W in the antenna circuit by means of switch 15 is described for long wave C. WV.; and likewise by increasing the inductance of the secondary by connecting coil units 65, 66, 67 in the secondary circuit by means of switch 46.

By means of the wave length and the i wave character switches, the arrangement may be readily changed to permit reception of waves of the desired character in either the range designated as short (300 to 900 j meters) or that designated as long (800 to 3,000 meters).

The more accurate. tuning will then be done by adjusting the knob 1. This will simultaneously vary the capacity and inductance. The variation lof the capacity is obtained by rotation of one set of the condenser plates by means of gears 79, 80 and the variation of the inductance 3 by means of the rotation of good conducting sheet metal shields 82, 83, 84, 85, 86 connectedto gearing 79, 81.

In the illustration live shields are used, viz 82 located between coil units 351 and 352;

83 located between 352 and 353; 84 located between 3IA and 315; 85 located between BLG and 3m; and 86 located between 3LB and 3L. Shields 82 and 83 effect the variation of the inductance of the lshort wave primary coil and 84, 85 and 86 come into action only for long wave reception.

The apparatus shown in the diagram may all be conveniently containedv in a rectangular box 90, (Figs. 4, 5 and 6) the top, sides and rear end being removable from the front 91 and base 91 upon which the apparatus is mounted in order to permit of inspection. A convenient arrangement for fastening the separate portions comprises a long rod 92 (preferably one on each side of the case) extending from the front to the rear where it passes loosely through a hole in a member' 93 which is fastened to a frame work 94. The end of the rodi-,is threaded and screws into a suitably locatetlf nut in the rear end of the casing. This arrangementpermits the rods to be loosened to allow the separation of the casing,fwithout withdrawing and reinserting the rods which is a troublesome matter in a casing containing numerous wires and considerable apparatus.

As shown in Fig. 6, two knobs are provided in the upper part on the front panel of the casing, one for shiftin f to Spark, Off and 0. W. and the ot er Long Waves Off, and Short Waves as indicated on the plates 95, 96. As the knobs correspond to members 4 and 5 of Fig. 1 they are designated by the same reference characters. A dial 97 mounted on the front of the cabinet is rotated by the adjusting knob 1 and has two scales, one for long waves and the other for short waves, the divisions being substantially equal for equal wave length differences. A pointer 98 cooperates with the scale and is moved up and'down by means of the knob 5 which has a pivoted extension 99 (Fig. 4). Said pivot extension is connected by a link 100 to a pivoted link 101 (Fig. 7) attached to the pointer and also a link 102 (Fig. 11) having a roller 103 for operating a structure 104 embodying both switches y15 and 46 of Fig. 1. In Fig. 11 a side view of two double throw switches is shown, the six wires fastened in the insulating block 105 of a member 106 comprising one half of each of switches 15 and 46. The other six wires are like those shown and the same type of switch is used for the two and three pole double throw switches 25 and 31.

The knob 4 also has a pivoted extension 107 connected to a link 108 (Fig. 4) which controls a switch structure 109 in the rear of the cabinet, which corresponds to switches 25 and 31 of Fig. 1.

The two telephone terminals 57, 58 are mounted onl the front of the cabinet. Besides the parts mentioned as shown in Fig. 6, a second knob 110 is provided for fine adjustments. The front view of the apparatus (Fig. 6) shows clearly the simplicity of thesadjustments compared with that of the us'uahcommercial device for similar purposes. In Fig. 7 a detail of a'convenient form of index pointer and connection is shown comprising aA housing 111, pointer 98 slidably -fitting in the housing said pointer having a portion cut away at the top and drilled to receive a staple 112 which connects with link 101. This-simple arrangement permits the members to be linked together and the link to be retained by the housing when it isattached to the casing.

Figs. 8 and 9 show details 'of an assembly of the main dial knob. 113 is a bearing fitting yin the front end 91 of the cabinet. The bearing has a shoulder 114 beneath the dial and a threaded end 115 protruding into the cabinet. A nut 116' cooperating with the threaded end permits the bearing to be clamped in the cabinet. The dial v97 has a central circular opening .somewhat smaller than shaft 117 and a projection 118 flattened on opposite sides extends through said opening. Two diagonally-opposite, threaded pins 119 are riveted at one end to the dial and filed off' smoothly. Itis desirable to adjust the dial without rotating the shaft and moving the members geared thereto toscrew125 by registering the nuts 123 with small diameter end 128 of the shaft.

suitable 'depressions drilled in the knob. A collar 126 is threaded on the bearing, and a gear 79, which actuates the adjustable elements as hereinafter described, is xed opha e longitudinal position of the shaft relative to the bearing is adjustable by changing the location of collar 126 which is fixed to the `bearing by means of set screws 127. To prevent these from beingentirely removed and lost the threads of the openings in the collar may be burred inwards after the set screws, which are short ones, have been inserted.

The fragmentary view of Fig. 10 shows the gearing arrangement. The gear 79connected to the main adjusting knob lmeshes with a larger gear 80 (about two to one ratio) connected with the variable condenser 2. As approximately 180o of rotation of the variable condenser are required for changing from maximum to minimum, the rotation of the knob from maximum to minimum will be almost 360 and the dial 97 will be graduated around substantially the entire periphery. The smaller gear 79 meshing with the large condenser gear 80 enables fine adjustments to be made by means of the knob 110 which is connected to it. A segmental gear 81 which controls the movementv of the shields 82, 83, 84, 85, 86 also meshes with gear 79. rlhe shields are fitted between the pivot shaft 81 and a bar 81l which is bolted to the middle of the segment gear, slot 129 being provided to permit adjustment of the bar.

In the assembled structure as shown in Figs. 4 and 5, the coil unitse are mounted in a rack in the front of the upper portion of the cabinet. Fig. v17 shows the front panel 130 by means of which vthe `units are secured to the front 91 of the cabinet. The frame has four slots 131 for receivg 131. Anfinsulating bushing 140 su ing bolts 132 which` ass through the front of the cabinet an tubular spacers 133 thus supportin the rack some distance from the front of t e cabinet. All of the coil units described with reference to Fig. 1 are held between front anel 13() and a rear panel `134 bymeans of bolts passing through suitable holes 135 in the panels. A number of tubular spacers 136, 137, 138 and 139 (Fig. 4) are placed on the bolts to separate the various sections of the coil unit assembly. The, pivot shaft 81 foor segment gear 81 is fitted in bearings in the front and rear panels 130 and 134 and projects through the front,

sufficiently to permit the segmental gear to be clamped thereto. To mesh the geai` 79 and segment `80 in a. proper manner the entire rack and segment earQ--may be move ...due to the provision o? the-,-:slots )'unds Certain portions of the pivot shaftlffSl' to prevent electrical connection with the shields82, 83, 84, and 86. At one side each bf the panels 130 and 134 are slotted at 141 to receive an insulating strip 142 Fig. 4 having a number of holes in which conductors are inserted for making connections to the coil units and with the other parts of the electrical circuits.

A particular feature of the mechanical struction of the receiver is the method of construction of the coil units which. is shown in Figs. 12 to 16. The coils are flat preferably of a single layer and spirally wound as shown in Fig. 14. A convenient method of winding such coils shown in Fig. `15 utilizesl a pairy of adjacent circular plates 143, 143 bevelled on the periphery of the adjacent faces. The lates are slidably mounted on a rotatable s aft 144 and pressed together by means of springs 145, 145 fitted between the platesand collars 146, 146 on the shaft. A turn ofwire which has a thin covering of insulation will be coiled on the shaft which will then be rotated at a suitable speed and the wire will be ressed into the space between the plates and), drawn down against the preceding turn. The spring pressed Iplates effectually prevent overlapping of the turns and a flat coil may be quickly wound to the desired size. A portion of the `inner turns will be unwound to form a lead 155 as shown and the second lead 156 will also v and a notch 147 for the shaft 81. To similar tothe ordinary rotatin late vaassemble the unit one of the sheets having riable condenser it will be descri e more or the contour mentioned is placed on the bench, and a second sheet 148 (Fig. 16) is placed thereon, a layer of adhesive being applied to the adjacent surfaces. Sheet 148 which is the coil holder has a circular opening 149 adapted At0 receive the coll and a pair`of notches 150, 151 at the side for outlets for the terminals. The third sheet- (Fig. 12) 152 has a small circular opening 153 and an inclined slot 154. This sheet after applying adhesive thereto is placed on the coil unit sheet 148. As shown in Fig.`12, space for the terminal 155 extending from the inner turny of the coil is provided by slot 154 so that the terminal wire does not prevent the sheets from lying iat against each other. As shown in Fig. 12 slot 154 of plate 148 and notch 150 over- .la-p slightly and the terminal 155 is drawn through this overlapping space and thence extends through notch 150 of the central plate to provide a lead as shown in Fig. 13. The other terminal 156 extends into opening 153 and similarly through an overlapping space between 'it and notch 151 and out through the notch 151. In .this manner a fiat durable coil unit is obtained with no exposed wires except the leads. These coil units may be connected up in various ways and used for various purposes for example, as previously described.

-Wherever movable conducting metal shields are used these will be placed between the units during assembly. An improved construction is shown inv Fig. 18 to prevent binding and friction which occurs due to slight variations in the thickness of various ortions of an assembly of coil units. If t e shields are fixed to the shafts 81 or 81" it has been found that even with good mechanical workmanship it is difficult to move the shields readily due to binding. In `the present construction theshields have lugs 157, 157 on opposite sides with V-shaped notches the distance between the notches being such that the discs are quite loose between shafts 81 and 815. No rigid connection will beutilzed between the-shields and the shafts, so that the-,j shields during their rotation are free Vto assume 'a horizontal position in which vthe friction is least.

In the illustration the shaft 81 is the pivot shaft about Whichthe shields are turned by the movementvof the stub shaft 81" Whic is bolted tothe segment gear 81. This enables the shieldjtovfbe moved in such manner that it overlaps varioussections of the coil. 'The shieldacts as a short-circuited secondary to the .coilunit and the inductance is progressively-reduced` as the shield is moved to cover various sections of the coil. Although the variable condenser is quite less in detail as several novel features are embodied therein. It is fastened to the front ofthe cabinet below the coil unit rack by means of bolts 158 Fig. 6 in much the same manner as t-he coil unit. The bolts pass through slots 159 in the front su ort 160 of the condenser (Fig. 21) whici is spaced from the front of the cabinet. The provision of the slots permits the condenser to be moved so that its gear 80 will mesh properly with the main gear 79.

Considerable difficulty is encountered in properly aligning the bearings of a variable condenser and in some cases when the bearings in use get out of alignment the rotation of the movable plates is seriously hindered. In the construction shown the condenser shaft' 161 has two portions 162 which fit in the bearings 163 located at each end. Instead of having a considerable length of the shaft in contact with the bearings each end 162 is formed as a short stub which has for example, a bearing surface only about 1/3, of an inch long. Should the bearings get out of alignment slightly the binding effect produced will be greatly minimized by having a small bearing surface.

The gear 80 Fig. 19 is fixed o`n the shaft 161 by fastening it to an insulating plate 164 fixed on one endA of the shaft. The movable plates 165 (Fig. 23) are keyed to the shaftin the usual manner andseparated by washers 166 Fig. 19. The keys 167 Fig. 23 being near the center of the shaft considerable force must be applied thereto to rotate the .plates and loose play results in due time with the ordinary construct-ion which is undesirable in a condenser for this pur pose as the condenser setting will not be correct for the dial reading. This is avoided in the present construction by providing a block of several plates 168 at one end of the condenser having openings at some distance from the center of the shaft for receiving a pin 169 which is screwed into the openings. When the shaft 161 is rotated through gears 79 and 80 the force necessary to turn it will be applied through the pin 169 and this being a considerable distance from the center the wear will be decreased and the loose play for a given amount of wear will be lessened.

Gear 128 is located in the condenser and adjacent to the gear 80, thecfront panel 160 of the condenser having a bearing 171 for receiving the shaft 172 of this gear. The rear end of the shaft 161 has a projecting end 173 of small diameter slotted to receive a coiled spring174 which has its other end tted in a slotl of the post 175 so that :1 slight spring pressure is exerted against the rotation of the condenser inwone direction.

The st-ationary plates 176 are assembled on rods 177 with spacers 178 so as to lie be-v i' tween the movable plates.

If the condenser capacity and the induetance both vary in uniformity as they are rotated through a certain angle the wave length variation will not vary proportionally through the entire range. The markings on the dial corresponding to equal changes of wave length will therefore progressively change, being large at one end and very small at the other. In Figs. 22 and 23 I have shown one method of substantially equalizing the spacings of the scale readings. The fixed plates 176 and the rotating plates are especially shaped so that for each spacing, for example, 10, on the scale the vwave length changes, the same amount, for

example, 100 meters. That is, knowing the inductance of the tuning coil (which with the shield i-nductance shown is not a straight line function) at each point' I compute the necessary capacity for the wave length desired at that position of the dial. A suitable shape of movable plate or stationary plate or combination of both is then plotted which in various positions gives the necessary overlapping surface area in eachv position. In Figs. 22 and 23 both the stationary and the movable plates are specially formed, the stationary plate having a segmental opening 177 and the movable plate having a somewhat similar segmental opening 17 8. If the plates are in position so that the openings correspond the condenser is in maX- imum position. During the first part of the rotation toward the right the capacity decreases rapidly as the forward ends`17 9 and 180 are both moving away from their cooperating surfaces. After rear end 181 passes edge 182 of the stationary plate the variation is more gradual as the movement of the portion 180-181 has substantially no effect. B the time edge 180 reaches the edge 183 the large segment 184 only slightly overlaps the large segment 185 of the stationary plate. The variation of capacity through the remainder of the 180 movement then proceeds at a slower rate.

In Figs. 24, 25, 26, 27 a coil unit is shown with a special shaped shield adapted to be utilized with the ordinary variable condenser having semi-circular plat-es. The gearing will be such that the condenser rotates 180 while the shield rotates approximately 27 0o. By this modification the same result may be obtained as with the special condenser just described. In the initial position (Fig. 24) the inductance is maximum as the shield scarcely overlaps any portion of the coil. During the rst 909 rotat'ion the inductance is decreased as determined by the extent of overlapping `shown in Fig. 25. In the next 90o the inductance decreases further as determined by the degree of overlapping shown in Fig. 26 and vductance and the movable condenser plates for varying the capacity are both located on the same shaft. The movable 'shields are of substantially the same shape as those shown lin Figs. 24; to 27 and a similarly shaped movable condenser 4plate is also used to seeure equal wave length variations for equal amounts of rotation. Such an arrangement may be utilized in thev apparatus heretofore described to eliminate the necessity for gearing `and may also be utilized as a tuner in any receiving set. The arrangement will also utilize 27 0o dial and have the advantage of greater rotation in passing from minimum to maximum Aand equal wave length changes for equal rotation. The stationary 'condenser plates 200 and the coil units 201 are mounted on two supporting rods 202, 203 and spaced apart by suitable distances by washers 204. Front and rear end members 205, 206 are fastened to threaded ends of the rods by means of nuts. As shown-in dotted lines in Fig. 28 the upper ends of these stationary members are semicircular and the lowest ends are square so as to permit the members to be litt-ed on the supporting rods. The rotatablev elements are mounted on a shaft 207Y located in bearings near the top of the end members and spaced from the supporting rods a sutiicient distance to permit the rotating elements to be turned. Any appropriate means may be used for fastening the shields and condenserplates to the shaft. The arrangement shown utilizes spacing washers 208 between the condenser plates 209 and clamping nuts 210- on a threaded portion of the shaft, which y obviates the disadvantage of keyways and keys and permits lateral adjustment. The shields 211 which are keyed to the shaft are then located in the proper position by means of washers which may be loose enough to permit some lateral movement, and avoid binding. The construction of the coil units may be similar to that shown in Fig. 12 and therefore need not be particularly described. A single'adjusting knob 212 will be fitted to the shaft in any appropriate manner.

In Figs. 4 and 5 a desirable arrangement in the cabinet forall of the apparatus is shown. The condenser anoL coil unit rack with the gearing are located in thefront as described. At the rear the rectangular frame 94`Fig. 5 is provided which is divided into two parts by an intermediate V shaped strip 190. The plate battery 13 is fitted into the lower portion in an upright position so that it may be readily inserted and removed. In the upper portion the two dry cells forming the filament battery are in- -during the third 90 decreases rapidly to a `serted,'tl1 ese preferably lying'on their sides. Two shelves 191, 192 are attached on top of the frame 94. The shelf 191 has the two transformers'S and 5l, attached thereto and lthe condensery and 54 are attached on top of the transformers. The switch 109 is also mounted on this shelf in the-position shown.

AOn the other shelf are located sockets 193,

-194 and 195 Fig. 4 for lthe three vacuum tubes ywhich are mounted in an upright j positiony` The filament rheostat is also fastenedfto 192 in 'an upright position. The yarrangement shown gives a compact receiving unit and when the top and sides are removed all necessary portions are easily accessible. v

Having described my invention, what I claim is: .1. In radio receiving apparat-us the Scombination of a single adjusting' member, a

' receiving circuit having tuning elements op- "dial cooperatively associated with said adjusting elements having substantially equal Wave length diierences.

- l 2. A tuner comprising a common rotatable 'movement vof the control member and of the lWave length to which the tuner is tuned.

3. In radio receiving apparatus a tuner and a continuously variable inductance, said 'capacity and inductance each comprising a series of coacting pairs of flat parallel mem-v bers movable relatively to each other, and a single adjusting member for the movable members of the inductance 4and capacity said movable inductance and capacity members shaped so that a straight line relationship is obtained bet-Ween the movement of the said single adjusting member and the Wave" length of the tuner.

4. A tuner comprising an inductance and a capacity and unitary rotatable means for simultaneously and continuously varying both inductance and capacitance so that for equi-angular movements of said rotatable means substantially equal changes in the Wave length of the tuner result.

. ALFRED N. GOLDSMITH.

comprising a continuously variable capacity 

